Abstract

High resolution spectra of the 4ν1 and 5ν1 OH-stretch overtone and the weak 4ν1+ν2 combination band of transient HO35(37)Cl in the energy range 12 500–16 500 cm−1 have been recorded using ultrasensitive intracavity laser absorption spectroscopy (ICLAS). For this investigation, two different spectrometers, a titanium:sapphire and a dye-jet ICLA spectrometer have been employed. We report line assignments for both isotopomers, refined Dunham parameters, and the spectroscopic constants for the excited rovibrational states. Strong and weak Fermi-type resonances as well as Coriolisinteractions at ≈65%–85% of the dissociation energyE0 have been found and the role of dark perturbers is discussed. The dark 2ν1+3ν2+3ν3 state has been analyzed and identified to be the perturber of 3ν1+2ν2. From the detailed analysis of the experimental data the anharmonicity parameters of the asymmetric stretch ν3 are refined. The 5ν1 band at about 85% of E0 has been found to be strongly mixed with the 4ν1+2ν2+ν3 zero order vibrational state, and both states are coupled to other background states by additional (weaker) interactions. The extent and the magnitude of perturbations in all Ka bands of the 5ν1/4ν1+2ν2+ν3 system and additional interactions with other background states may be regarded as the signature of the onset of efficient but restricted intramolecular vibrational energy redistribution (IVR) in the overtone spectrum of HOCl. The intramolecular dynamics of this small molecule after coherent short pulse excitation of the 5ν1 zero order state is discussed in terms of a simple tiers model.